When a television set owner is a subscriber to a cable television system and also possesses a videocassette recorder (VCR), he may be required to connect to the cable system via a cable decoder box (also called a CATV converter, or a set-top converter). This connection may be required, because in these systems, many cable channels (i.e., the so-called premium channels) are scrambled (i.e., encoded or encrypted) and must be descrambled (i.e., decoded or decrypted) in the cable box. The cable box descrambles the premium channel and converts its RF carrier frequency from its assigned cable channel frequency to a cable box output frequency, normally that of channel 2, 3, 4, or 5 for reception and recording by the VCR, or display by the television receiver. In such an arrangement the viewer may have as many as three remote control units for controlling the video equipment (i.e., one each for a television set, a VCR, and the cable box).
Recently, a programming simplification system known as VCR PLUS.TM., manufactured by Gemstar Development Corporation, Pasadena, Calif., has become available. Briefly, the apparatus of the VCR PLUS.TM. system resembles a standard remote control handunit. The handunit is preprogrammed with the codes for controlling the VCRs and cable control boxes; of many manufacturers. The handunit is then programmed by the user with a unique code comprising 1 to 8 digits, which code corresponds to a particular television show broadcast on a given channel, at a given time and date, and having a given duration. A television show which is broadcast at the most popular viewing time (for example, 7 pm) may have a code which comprises only 1 digit. Conversely, a television show which is broadcast at the least popular viewing time (for example, 3 am) may have a code which comprises the full 8 digits. These codes are printed in the channel guide section of the viewer's local newspaper along with the normal time and channel information. After entering the unique 1 to 8 digit code for a particular television show to be recorded, the user places the handunit in a cradle mounted on his VCR to ensure that the handunit is in the proper orientation for transmitting data to the IR (infrared) receiver of the VCR and to the cable box. At the proper time, the VCR PLUS.TM. handunit transmits IR codes to the cable box to turn it on and tune it to the desired channel, and to the VCR to turn it on and program it to record the desired television show.
Unfortunately, the stand alone VCR PLUS.TM. handunit operates in an "open-loop" mode. That is, the VCR PLUS.TM. handunit has no way of knowing if its commands were actually received by either the VCR or by the cable box because no feedback signal to the VCR PLUS.TM. handunit exists. This situation causes the following problem. Most cable box IR remote control command formats do not include separate commands for POWER ON and POWER OFF. Rather, it is common practice for cable box manufacturers to program the cable box such that the POWER ON/OFF remote control command is a toggle function. If the command is received while the cable box is "on" then it will turn off. If the command is received while the cable box is "off", then it will turn on. With an "open loop" type of system, such as implemented in the VCR PLUS.TM. handunit, the controller has no way of knowing if the cable box is "on" or "off". Thus, if the cable box is already "on", the command to turn it "on" in preparation for transmitting it a channel change command will in fact turn the cable box off. As a result, the desired channel change will not be accomplished, and the desired program will not be recorded.